C9orf72 and amyotrophic lateral sclerosis: Familial ALS accounts for the remaining 10% of patients and has been linked to mutations in genes such as Cu, Zn-superoxide dismutase 1 (SOD1), chromosome 9 open reading frame 72 (C9orf72), fused in sarcoma, and TAR DNA-binding protein 43 (TDP-43) [2].